Hellbender

SPECIES INFORMATION

Classification

The hellbender (Cryptobranchus alleganiensis alleganiensis) is classified as an amphibian. The hellbender is a member of the Cryptobranchidae family (Neto 2019). Cryptobranchus alleganiensis alleganiensis is the only extant member of the Cryptobranchus genus (Petranka 1998). See Figure 1 for the full taxonomy of the hellbender. 

Domain: Eukaryota

Kingdom: Animalia

Phylum: Chordata

Class: Amphibia

Order: Caudata

Family: Cryptobranchidae

Genus: Cryptobranchus

Species: C. alleganiensis

Figure 1. Taxonomic hierarchy of hellbender (Frost 2022).

Description

The eastern hellbender is a large, long-lived paedomorphic salamander (Unger 2013; Neto 2019). They are fully aquatic (FWS 2024). Hellbenders average 50 cm in total length. Specimens have been recorded up to 76 cm (Petranka 1998). Most populations have little to no sexual dimorphism (Nickerson and Mays 1973).  Hellbender colorations vary. According to Mayasich, they exhibit dark green to dark grey dorsally and are lighter on their ventral side (2003). Petranka states that they vary from grayish to reddish brown and may have darker spots or mottled patches along the back (1998). They have an elongated body and short limbs with 4 toes on the front feet and 5 on the hind (Mayasich 2003). Hellbenders exhibit a flattened head and body and rounded snout (Williams and Hall 2016). They have a pair of small, poorly-developed eyes (Petranka 1998). Hellbenders have prominent lateral folds. This loose fold of skin runs from the base of the neck to the tail on both sides of the body and increases the skin's surface area, which helps the hellbender breathe (Williams and Hall 2016). Hellbenders employ cutaneous gas exchange and do not need gills, yet they retain rudimentary gills as part of their incomplete metamorphosis. The body is mucous-covered. These secretions may deter predation (Mayasich 2003). 

NATURAL HISTORY

Geographic Distribution

Hellbenders range from southwestern New York, westward to southern Indiana and Illinois, and southward through the mid-Atlantic states to northern Alabama and northeastern Mississippi (Petranka 1998). In North Carolina, the hellbender occurs in mountain streams of the Ohio and Tennessee watersheds (Williams and Hall 2016). 

Home Range

Hellbenders have small home ranges, but studies suggest the size is highly variable and likely dependent on several density variables: prey availability, stream size, and structure availability with a high emphasis on the number of large rocks for shelter (Hecht et al. 2019). Burgmeier suggests the average size is 28m2 (2011). Humphries and Pauley measured home ranges between 198m2 and 346m2 (2005).  The hellbender does not migrate. Hellbenders have been observed to spend the majority of their time under the same rock once they have established it as their den, traveling a maximum of 10m from the rock (Humphries 2005).  

Territorial Information

Hellbenders spend their time alone under rocks and will defend their den (Nickerson and Mays 1973). Hecht et al suggest that physical spacing is highly dependent on the number of large rocks for shelter (2019). Other density variables include prey availability, stream size, and structure availability (Nickerson and Mays 1973). Humphries and Pauley observed hellbenders emerge just after dark and roam 10 to 20 meters from their rock (2005). 

Habitat

Hellbenders require cool, swift-flowing water with large rocks and an abundance of crayfish (Humphries and Pauley 2005). Adult eastern hellbenders spend most of their life under large, flat rocks that shelter them (FWS 2024). According to Hecht et al, the ideal stream substrate for hellbenders is large rocks with interstitial space and a base of coarse gravel (2019).  Often they are found just upstream of riffles in calm water 15 to 56 cm deep (Humphries 2005). Humphries most often observed hellbenders at depths 30 cm or less (2000). Hellbenders require specific water conditions. Temperatures must range from 9.8 degrees C to 22.5 degrees C. PH measurements need to be 7.6 to 9.0. They require oxygenation levels of 8.4 to 13.6 mgL-1 (Nickerson and Mays 1973). 

Niche

Hellbenders are secondary consumers. Crayfish are their major food source (Humphries and Pauley 2005). Aquatic invertebrates and fish were the majority of prey based on the stomach contents of hellbenders (Nickerson and Mays 1973). Mayasich noted that hellbenders typically seize prey with quick sideways movements (2003). The hellbender is mostly nocturnal and relies on touch and smell to catch food (Williams and Hall 2016).

Mortality Factors

Hellbenders are most at risk of habitat fragmentation due to dams (Nissen 2023), the spread of disease, increased UVB radiation, and habitat degradation (Unger 2013). Additional mortality factors are due to increases in stream impoundment, siltation, gigging activities, scientific collection, illegal harvest, canoe traffic, agriculture runoff, predation by non-native fishes, and thermal pollution (Unger 2013). Habitat degradation, siltation, contaminants, and disease affect hellbender mortality (Neto 2019). Dams and impoundments reduce swift water and riffles while decreasing oxygen availability. Siltation reduces cover, nest sites, and prey (Mayasich 2003). Mining, road construction and maintenance, and logging cause extensive sedimentation (IUCN 2022). The increased fine gravel from human-caused erosion affects site occupancy negatively since it covers the interstitial spaces of rock and coarse gravel, which are important as nest sites, and for shelter and food production (Keitzer 2013). Water quality is important to hellbender's health. The cutaneous gas exchange makes them very sensitive to water quality and they easily absorb toxins. Water-dissolved chemical pollutants and industrial and agricultural drainage destroy eggs and larvae (Green et al. 2014). Death and injury can result from fishing. Hellbenders can be hooked while angling for game fish such as trout. Hellbenders are generally intolerant of heavy recreational use of their habitat (Nickerson and Mays 1973). There is some collection for live trade of the species and overutilization for collecting affects hellbender populations. Pike, musky, turtles, and water snakes prey on hellbenders (Nickerson and Mays 1973).

REPRODUCTIVE INFORMATION

Breeding Season

Hellbender breeding varies by latitude and stream system but is most often from mid-August to mid-September (Petranka 1998).

Mating Habits

Hellbenders exhibit a seasonal burst of movement for breeding activities (Petranka 1998). The male will create a nest. They favor rocks partially embedded with a downstream entrance (Humphries and Pauley 2005). Multiple females may visit the nest. They will release pearl necklace-like strands of eggs. The male will fertilize the eggs by releasing milt into the strands. This external fertilization is unusual in salamanders (Nissen et al. 2023). 

Number of Offspring

Once per year, females deposit between 200 to 1400 eggs. The average clutch size is 300 per nest. (Kleopfer and Ruthenberg, 2024).  Survival for eggs and larvae is low (Taber et al 1975). Hatching occurs 4 to 8 weeks after fertilization. Incubation time depends on water temperature (Kleopfer and Ruthenberg, 2024). Eggs hatch larvae 27-33 mm long. These hatchlings retain a yolk sac (Petranka 1998). The growth rate is approximately 3 inches per year (Williams and Hall 2016).

Care of Offspring

Males will remain with the brood and defend the nest (Mayasich 2003). Larvae undergo an incomplete metamorphosis at 18 months (Mayasich 2003).  

CONCLUSION

Current Status

According to Mayasich et al, hellbenders are threatened (2003). According to IUCN, hellbenders are listed as Vulnerable because of significant decline between 30–50% over the past 30 years due to the impacts of disease and widespread habitat loss and degradation throughout much of its range (2022). The hellbender disappeared from many localities of its range between 1935 and 1965 (IUCN 2022). Over a 20-year study, populations declined by 77% (IUCN 2022). USFWS estimates 126 subpopulations are healthy while 219 are declining (2018). Many hellbender populations occur in national forests, state forests, national parks, or other public lands. These public lands offer good potential for protecting habitat. Some of these areas are at risk of negative impacts from upstream activities (IUCN 2022). The St. Louis Zoo maintains a captive breeding program for this species (IUCN 2022). 

The Virginia Department of Wildlife Resources supports hellbender conservation through multiple research studies, deployment of nest boxes, and stream habitat restoration. In 2019, the Virginia DWR tested artificial shelters called nest boxes. From 2016–2020, researchers used about 500 nest boxes at 12 different sites across 5 different streams. Nest boxes could help prevent population declines and promote population growth (Kleopfer and Ruthenberg, 2024).

A characteristic of population declines across hellbender’s range is a shift towards large, old individuals with few representatives in younger size/age classes. This suggests that reproductive failure and/or a lack of juveniles joining the population may contribute to hellbender population declines. Hellbender reproductive and juvenile ecology are poorly understood so data obtained from nest boxes is critical for managing hellbenders (Kleopfer and Ruthenberg, 2024).

Future Outlook

Hellbenders have little tolerance for environmental change. Therefore, recovery efforts should preserve headwater streams and mitigate sedimentary runoff and erosion. Research suggests preserving highly forested, low-impacted watersheds will be important to conserving hellbenders (IUCN 2022). A salamander chytrid fungus, Batrachochytrium salamandrivorans, has caused declines in European fire salamanders. If Batrachochytrium salamandrivorans were introduced to the US, hellbender populations could rapidly decline (IUCN 2022).

Legal policy, agency administration, and politics will affect future management practices and status projections for hellbender. A recent case, Center for Biological Diversity et al. v. U.S. Fish and Wildlife Service, can be used as an example.

The Center for Biological Diversity and other organizations, collectively “Waterkeeper”, had submitted a petition under the ESA regulations requesting that the eastern hellbender be listed as either threatened or endangered. The Service issued a positive 90-day finding that the Waterkeeper petition presented substantial evidence that a listing of the hellbender may be needed. Nevertheless, the Service failed to make a listing determination. Waterkeeper sued the Service to get a determination. The Service and Waterkeeper agreed that the Service make a listing determination by September 30, 2019. The Service found that listing the eastern hellbender was not needed. In its determination, the Service stated:

“Rangewide, the number of extant populations is predicted to decrease by 2 to 52 percent over the next 10 years, and then slightly decrease from year 10 to year 25 under both scenarios, with the “most likely” scenario skewed toward the reasonable worst plausible scenario. Despite these overall losses, multiple healthy populations over a broad geographic range are predicted to persist over the next 25 years (55 to 178 healthy populations, representing a 57-percent decrease to a 40-percent increase from current conditions).” 

Therefore, the Service concluded that the eastern hellbender was not endangered or threatened throughout all or a significant portion of its range and that listing was not needed (United States District Court Southern District of New York 2023).

Waterkeeper challenged the Service’s finding. They argued that it failed to rely on the best scientific and commercial data. The Court ruled in favor of Waterkeeper and held that the Service’s determination is not valid (United States District Court Southern District of New York 2023). The U.S. Fish and Wildlife Service’s 2019 denial of Endangered Species Act protection for the eastern hellbender salamander was arbitrary and unlawful. The judge instructed the agency to make a new decision consistent with the law.

Listing would give the hellbender Endangered Species Act protections. This would greatly affect the resources available, research, and management practices for hellbenders and ideally improve future status projections.

LITERATURE CITED

Burgmeier NG, Sutton TM, Williams RN. 2011. SPATIAL ECOLOGY OF THE EASTERN 

HELLBENDER (CRYPTOBRANCHUS ALLEGANIENSIS ALLEGANIENSIS) IN INDIANA. Herpetologica 67(2):135-45.

Frost, D.R. 2022. Amphibian Species of the World: an Online Reference. Version 6.1. New York, 

USA. American Museum of Natural History. 

Green, D.M., Wier, L.A., Casper, G.S. and Lannoo, M.J. 2014. North American Amphibians: 

Diversity and Distribution. University of California Press.

Hecht, K. A., Freake, M. J., Nickerson, M. A., & Colclough, P. (2019). Hellbender salamanders 

(Cryptobranchus alleganiensis) exhibit an ontogenetic shift in microhabitat use in a Blue Ridge physiographic region stream. Copeia, 107(1), 152-159.

Humphries WJ and Pauley TK. 2000. Seasonal changes in nocturnal activity of the hellbender, 

cryptobranchus alleganiensis, in West Virginia. J Herpetol 34(4):604.

Humphries WJ and Pauley TK. 2005. Life history of the hellbender, cryptobranchus

alleganiensis, in a west virginia stream. The American Midland Naturalist 154(1):135-42.

IUCN SSC Amphibian Specialist Group. 2022. Cryptobranchus alleganiensis. The IUCN Red 

List of Threatened Species. International Union for Conservation of Nature and Natural Resources.

Keitzer SC, Pauley TK, Burcher CL. 2013. Stream characteristics associated with site occupancy 

by the eastern hellbender, cryptobranchus alleganiensis alleganiensis, in southern West Virginia. Northeast Nat 20(4):666-77.

Kleopfer, J.D. and Ruthenberg, J. 2024. Virginia Department of Wildlife Resources Species 

Profile Database. 

Mayasich, J. M., Grandmaison, D., & Phillips, C. (2003). Eastern hellbender status assessment 

report. University of Minnesota Duluth.

Mayasich, J., Grandmaison, D., & Phillips, C. (2003). Conservation Assessment for Eastern 

Hellbender (Cryptobranchus alleganiensis alleganiensis) Daudin.

Neto JGDS, Sutton WB, Freake MJ. 2019. Life-stage differences in microhabitat use by 

hellbenders (cryptobranchus alleganiensis). Herpetologica 75(1):21-9.

Nickerson, Max & Mays, C.E.. (1973). The hellbenders: North American giant salamanders.

Nissen BD, Freake MJ, Nolan E, Hardman RH, Sutton WB. 2023. Evaluating translocation 

success of wild eastern hellbenders (Cryptobranchus alleganiensis alleganiensis) in blue ridge ecoregion streams using pre- and post-translocation home range sizes and movement metrics. PLoS One 18(4).

Petranka, James W. Salamanders of the United States and Canada (Washington, D.C.:

Smithsonian Institution Press, 1998).

Simanek, Kristin. 2021. Source NCTC Image Library. Accessed 10 April 2024. 

U.S. Fish and Wildlife Service [FWS]. 2024. Eastern Hellbender.

<https://www.fws.gov/species/eastern-hellbender-cryptobranchus-alleganiensis-alleganiensis>. Accessed 12 Jan 2024.

Unger SD, Rhodes, Olin E., Jr, Sutton TM, Williams RN. 2013. Population genetics of the 

eastern hellbender (cryptobranchus alleganiensis alleganiensis) across multiple spatial scales. PLoS One 8(10).

United States District Court Southern District Of New York. Center For Biological Diversity et 

al. v. U.S. Fish And Wildlife Service et al. Case 1:21-cv-05706-LJL Document 75

Virginia Herpetological Society. 2024. Eastern Hellbender. 

<https://www.virginiaherpetologicalsociety.com/amphibians/salamanders/eastern-hellbender/index.php>. Accessed 9 April 2024. 

Williams, Lori, and Hall, Jeff. 2016. Wildlife Profiles-Eastern Hellbender. North Carolina 

Wildlife Resources Commission.